Transistorized light flasher and testing circuit



March 28, 1961 G. H. RODGERS 2,977,581

TRANSISTORIZED LIGHT FLASHER AND TESTING CIRCUIT Filed Sept. 16, 1958 INVENTOR.

GEORGE HI P006525 "A TTOPNE% fli States P -1m -TRANSISTORIZED LIGHT FLASHER AND TESTING CIRCUIT This invention relates to electric light flasher circuits of the type utilizing coupled NPN and PNP transistors for developing an intermittent or fluctuating electric current such as to intermittently energize an electric lamp with a flashing action. The invention is applicable to indicator lights such as are .used on instrument panels of complex mechanism, as in airplanes, for providing a Warning indication of any fault or other condition occurring. in any of the several components-of such mechanism, requiringthe attention-of an operator. or attendant, and it is also applicable to barricade lights, such as are used for warning motorists to avoid barricaded areas where road repairs are in progress, or of dangerous roadway conditions or obstructions and to miscellaneous flashing signals, such as automobile turn signals etc.

The general object of the invention is' to provide an improved, simplified flasher circuit of this general type.

A more specific object is to provide a flasher lightunit having means for testing the operative condition of the flasher lamp thereof. i

. A further object is to provide an improved indicator light for instrument panels etc., having a flashing action and Ya means for instantaneously testing the operative condition ofits flasher lamp with maximum case.

Other objects and advantages will become apparent in the ensuing specification and appended drawing in which:

, Fig. 1 is a perspective view of a flasher light embodying the invention;

. ,Fig. 2 is a fragmentary sectional view thereof; and- Fig. 3 is a schematicdiagram ofmy improved circuit.

Referring now to the drawing in detail, and in particular to Fig. l, I have shown therein, as an example of one form in which the invention may be embodied, a flashing indicator light unit which, physically, embodies abarrel 5 havinga rear end in which is secured a base 6,with terminals 7, 7' and, 7"; and having a. forward end in which is mounted a lamp unit comprising a lamp socket 8, a lens cap 9 of transparent or translucent glass or plastic material, which may in some cases be of a red color toimpart warning red glow to the light flashes, and a lamp bulb 10 which may be a' small filament lamp adapted to operate on 28 volts. v.A flasher control unit, indicated generallyat 11, is mounted within the barrel 5 and connected to the lamp lll and terminals 7, 7', 7" as will be more fully described hereinafter.;

The unit 11, for mounting purposes, may include a small panel 12 of insulating sheet material, and a pair of discs or brackets 13 attached to the respective ends of the panel 12 and mounting them into the-respective ends of the barrel 5. Unit 11 also includes a pairrof transistors PNP and NPN and resistors 100, 100', 39K and 270 (see Fig. 3) mounted on both faces of the panel 12 and accommodated in the semi-cylindrical spaces defined within barrel 5 on respective sides of the panel. As indicated by their reference characters, the transistors are of'the NPNand PNP types, respectively. Referring now to Fig. 2, lamp bulb 10 is mounted in the socket 8 which is slidably mounted. in a-tubular collar 15 that is suitably mounted in the forward end of barrel 5. The annular base contact of lamp bulb 10 is yieldably supported by a washer 16 resting on a coil spring 17 which seats on a flange 18 constituting the bottom of socket 8; and the central contact of lamp 10 bears against the head of a sliding conductor pin 19 which is yieldably supported by a coil spring 20 and is slidably mounted in a contact sleeve 21, connected to a terminal 22. Sleeve 21 secures in assembly a stack of insulator washers 23, 24 and 25 and a pair of interposed contact rings 26 and 27 which are cored with small insulator washers so as to be insulated from sleeve 21. Contact rings 26 and 27 are provided with terminal lugs 26' and 27' projecting through the stack of insulators as illustrated for terminal 27'. The terminal 22 is connected, through a conductor 19' (Fig. 3) extending through barrel 5, to base terminal 7. Terminals 26' and 27 are connected respectively to control unit 11 and to a conductor 37 leading through barrel 5 to base terminal 7. Base terminal 7", connected to control unit 11 by a conductor 36, provides a connection between control unit 11 and a fault switch P (Fig. 3) which, when closed, initiates the flashing action. Switch F is located externally of the flasher unit shown in Fig. 1. For example, it may be associated with an airplane landing gear, to indicate either a retracted or an extended condition thereof (or to any other component requiring observation), as may be elected by the manufacturer of the airplane or other mechanism. Socket 8 is -suitably insulated from collar 15, as by means of an insulator sleeve 29, and is provided with. an axially projecting leg30 extending through a periph-- eral notch in insulator washer 23 and terminating in a. contact finger 31 which normally engages annular con tact 26 under the loading of spring 20. Manual pressure applied to lens cap 9 at the outer end of socket 8 is effective to shift the socket 8 to an alternate position wherein contact31 engages annular contact 27 and is freed from annular contact 26. Collector 34 of transistor PNP is connected through a conductor 35, a low vvalue resistor v100, a conductor 36, and terminal 7" to 1 ing observation by the pilot or other operator of the mechanism in which the indicator light is utilized, will result in the closing of switch. F which will establish a lamp energizing circuit through conductor 36, resistor 100, conductor 35, transistor PNP, conductor 32, terminal 26', contacts 26 and 31, and internal connections 14, 19, 22, 22' to terminal 7, whereby, when transistor PNP is conducting, a load current sufiicient to light the lamp 10 will be imposed thereon. This load current is an intermittent one, resulting in an on and off flashing of the lamp 10, as .will presently be explained.

To test the lamp 10, the operator presses against the lens cap 9, opening the circuit between contacts 26 and 31 and closing the circuit between contacts 31 and 27,v the latter being connected directly through connection 37 to the negative side of source 28v as indicated.

The base 38 of transistor PNP is directly connected by a conductor 39 to the collector 40 of transistor NPN. Forcontrolling the intermittent operation of the lamp circuit described above, the emitter 41 of transistor NPN is connected through a low value resistor 270 and a conductor 42to the negative side of source 28v through fault switch F, Thus the load current of transistor NPN, when conducting, will cause the collector 40 of transistorNPN to become more negative and a'corresponding drop in potential on base 38 ct transistor PNP will be effected. The connection 39 between NPN collector 40 and PNP base 38 is a direct one, i.e. without substantial resistance therein, the resistance being only that of the conductor 39 and no added resistance (asby the addition of aresistor) being utilized.

The base 43 oftransistor NPN is connected, at-44,- to a seriesconnection 45 between resistor 39K and the positive side of a capacitor, C. The negative side of capacitor C is connected, by a conductor 46 to the collector 34 of transistor PNP and, inparallel, to the connection 35 to the negative side of the circuit.

Resistor 39K is connected, at 47, to the connection 39 between the plate 38 of. transistor PNP and the collector 40 of transistor NPN. To this same connection 39 is-connected the emitter 33 of transistor PNP, through a conductor 48 and resistor 100 in series.

The resistors 100 and 100' are of low resistance value and may, as indicated by their reference numerals, be each of 100 ohmsresistance. The resistor 270 likewise is of low value but higher than the resistors 100 and 100', a suitable value in relation to the 100 ohm resistance of the latter resistors being 270 ohms as indicated by the reference numeral 270. The resistor 39K is of high value and, inrelation to the other values given above, may be 39,000 ohms as indicated by its reference. character 39K. The capacitor C, for the resistance values given above, may be of 25 microfarad capacity. The lamp may be a small filament lamp having a wattage of 1.12 watts. a

In the flashing operation, when the capacitor C is discharged, the transistors will be in non-conducting state. and the potential on NPN transistor base 38 will be. low (negative). When switchF is, closed, a small charging current will flow in the circuit including conductors 36 and 46, capacitor C, resistor 39K, conductor 47,, resistor 100 and conductors 48 and 26, gradually charging capacitor C and causing the base 43 of transistor NPN to gradually become more positive with. respect to its emitter 41, which remains negative, at a potential slightly above the negative side of current source 28%. As the base 43 becomes more positive, the resulting.

control current flow between emitter 41 and base 43 will render transistor NPN conducting, and collector current will flow in its collector circuit including conductors 25, 48 and 42 and resistor 270. The resistance value of the latter is sufficient to restrain this current at a relatively weak intensity, which is adequate, however, to maintain the potential on emitter 33 of tran-- sistor PNP at a high level while dropping the potential on plate 38 of. transistor PNP to amore negative valuewill drop exactly in step with. the drop in collector 40..

The action of transistor PNP therefore follows closely the action of transistor NPN, and as a positive bias thus is established on the emitter 33 of transistor PNP, the latter will become conducting to. alsuflicient. extent to light the lamp 10 and to simultaneously dischargethe capacitor C.

As. capacitor C loses its charge, thepotential on its positive side will drop, and plate 43 of transistor NPN will correspondingly become more negative, until the bias across this transistor in its emitter circuit will have been reduced to the point where the transistor becomes non-conducting. With thecollectorcurrentof-the transistor NPN thus cut off, the plate38- of transistor PNP by leakage current through the relatively low resistance of resistor 100., will 'gradually'be restored to a potential only slightly below that of terminal 22' at the;

. 4 positive side of current source 28v, thus cutting off the forward bias in the emitter circuit of transistor PNP and causing this transistor to become non-conducting and the lamp 10 to be extinguished. This restoration of positive potential on plate 38 proceeds relatively rapidly, while the positive side of capacitor C is held at substantially zero potential (i.e. the capacitor remains in a substantially discharged state) due to the high resistance value of resistor 39K. This completes a cycle of operation, with both transistors non-conducting and with capacitor C discharged. A new cycle of operation will immediately commence with the charging of capacitor C by the relatively weak current passing through lamp 10 and resistors 39 and 100 in series.

Iclaim:

1. In a flashing indicator light apparatus for automatic fault indication, in combination: a fault switch; a lamp; a test switch including a movable contact actuated by movement of said lamp and having a constant electrical connection with one side thereof, a first fixed contact on which said movable contact is normally closed, and

a second fixed contact constantly connected to one side of a voltage source, the other side of said lamp being constantly connected to the other side. of said voltage source; a PNP transistor arranged with its emitter and collector connected in series with said fault switch, lamp and source, whereby its load current may energize said lamp when said fault switch is closed; an NPN transistor; connections between the emitter and collector of said NPN transistor and said fault switch, said PNP transistor and said source, providing an NPN load circuit; a direct connection between the NPN collector and the PNP base in parallel with NPN load circuit providing therewith a biasing circuit whereby the PNP- transistor will be converted from a non-conducting to a conducting state by the load current from said NPN.

pacitor, with said NPN transistor being biased from a non-conducting to a conducting state as said capacitor is converted from a discharged to a charged state; the load current of said PNP transistor, when conducting,

being effective to simultaneously flash said lamp and discharge said capacitor and both transistors becoming non-conducting with the discharge of the capacitor; said test switch, when closed on. its said first fixed contact,

completing the flashing circuit and, when manually closed on said second contact, completing a direct circuit to said source bypassing said flasher circuit, for test-lighting said lamp, said current source constituting the sole source of current. for biasing said transistors.

2. A light flasher apparatus as defined in claim 1, in-

cluding a barrel in which said transistors, resistors,

capacitor and connections are encased; a lamp socket having a lens head enclosing said lamp; a collar in whichv said socket isslidably mounted; and resilient means acting between said collar and socket to yieldingly maintain said socket and headin a projected position, said collar being mounted in one end of said barrel, said movable contact being carried by the rear end of said socket, and said fixed contacts being mounted in the rear end of said collar.

3. A flashing indicator apparatus as defined in claim 2,. including. a basemember mounted in the other-end of said barrel and having terminals for connection to said fault switch and a current source.

4. In aflashing indicator light apparatus for automatic indication, in combination: connections to a' voltage source connection; a PNP transistor arranged with its emitter and collector connected respectively to said first fixed contact and to the other side of said fault switch to provide a load circuit wherein load current may energize said lamp when said fault switch is closed; an NPN transistor; means including a first low value resistor providing a connection between the emitter of said NPN transistor and said other side of the fault switch in parallel with said load circuit; means including a second low value resistor in series connecting the collector of said NPN transistor to the PNP emitter and to said first fixed contact to provide, with said NPN emitter-fault switch connection, a load circuit for said NPN transistor; a direct connection, without substantial resistance, between the NPN collector and the base of the PNP transistor for biasing said PNP transistor in response to current flowing in said NPN load circuit; a capacitor having one side connected to the PNP collector and a connection between its other side and the base of said NPN transistor;'and means including a high value resistor directly connected to said last mentioned connection and in series from said second low value resistor, providing a weak current path through said lamp and capacitor for charging said capacitor, there being a common connection between said high value resistor, the NPN collector, the PNP base and said second low value resistor, the latter being interposed in series between said PNP emitter and said common connection, with said NPN transistor being biased from a non-conducting to a conducting state as said capacitor is converted from a discharged to a charged state, and with the PNP transistor being correspondingly converted from a non-conducting to a conducting state by the load current from said NPN transistor when conducting, to the point where the load current of said PNP transistor will simultaneously flash said lamp and discharge said capacitor and with both transistors becoming non-conducting with the discharge of the capacitor; said test switch, when closed on its said first contact, completing the flashing circuit and, when manually closed on said second contact, completing a direct circuit to said source bypassing said flasher circuit, for test-lighting said lamp, said current sourceconstituting the sole source of current for biasing said transistors. I

5. A flashing indicator light apparatus as defined in claim 4, including a low value resistor in the connection between said fault switch and the PNP collector.

6. In a fiashing indicator light apparatus for automatic fault indication, in combination: connections to a voltage source; an indicator lamp having one side constantly connected to one of said source connections; a test switch including a movable contact connected tothe other side of said lamp and actuated by movement of said lamp, a

first fixed contact on which said movable contact is normally closed, and a second fixed contact constantly connected to the other of said source connections; a fault switch having one side connected to said other source connection; a first transistor of one semi-conductor type; means connecting the emitter and collector of said first transistor to said first fixed contact and to the other side of said fault switch to provide a power circuit wherein load current of said first transistor may energize said lamp when said fault switch is closed; a second transistor of an opposite semi-conductor type; means including a first low value resistor providing a connection between the emitter of said second transistor and said other side of the fault switch in parallel with said power circuit, a second low value resistor connecting in series the collector of said second transistor to the emitter of the first transistor and to said first fixed contact, to provide a load circuit for said second transistor; the connection between said first transistor and said other side of the fault switch ineluding a third low value resistor; a direct connection, without substantial resistance, between the collector of the second transistor and the. base of the first transistor for biasing said first transistor in response to current flowing in said load circuit; a capacitor having a side of one sign connected to the collector of said first transistor and, through said first fixed contact of the test switch, to the voltage source connection of the same sign; a direct biasing connection between the other side of said capacitor and the base of said second transistor; and means including a high value resistor directly connected to said biasing connection and in series with said second low value resistor, providing a weak current path for charging said capacitor, there being a common connection between said high value resistor, the collector of the second transistor, the base of the first transistor and said second low value resistor, the latter being interposed in series between said emitter of the first transistor and said common connection, with said second transistor being biased from a nonconducting to a conducting state as said capacitor is converted from a discharge to a charged state and with the first transistor being correspondingly converted from a non-conducting w a conducting state by the load current from the second transistor when conducting, to the point where the load current of said first transistor, acting in said power circuit, will simultaneously flash said lamp and discharge said capacitor and with both transistors becoming ncn conducting with the discharge of the capacitor; said test switch, when closed on its said first contact,

completing the flashing circuit and, when-manually closed on said second contact, completing a direct circuit to said source by bypassing said flasher circuit, for test-lighting said lamp.

References Cited in the file of this patent UNITED STATES PATENTS Winklepleck: Popular Electronics, September 1958, (pp, -76 relied on). t 

